Serological grouping of streptococci: A collective evaluation in six laboratories of three rapid methods

Abstract

Three serological methods for streptococci grouping: latex agglutination after pronase extraction (LAP), latex agglutination after nitrous acid extraction (LAN) and counterimmunoelectrophoresis after nitrous acid extraction (CIEN) were evaluated in six laboratories with 310 strains of streptococci. To reduce the possible influence of a particular laboratory, each serological procedure was performed in two different laboratories with identical protocols and strains. Between the three procedures, a total agreement of 81.3% with six identical results was obtained. Since only one discordant result was obtained in 12.2% (CIEN 4.8%-LAN 5.8%-LAP 1.6%) and two discordant results with two different serological methods in 2.6%, it could be concluded that agreement between the three procedures was 96%. For B (99 strains tested) and D(100 strains tested) groups, total agreements of respectively 95% and 92% were achieved. In conclusion, LAP, LAN, and CIEN gave equivalent results for streptococci grouping, but LAN was the most simple needing no heating, centrifugation, or electrophoresis equipment and lacking cross-reactivity of group C antibody.

Comparison of fluorescent antibody, bacitracin susceptibility, latex agglutination, coagglutination, and API 20S for identifying group A streptococci

“…Results with the Phadebact and SeroSTAT Group A reagents gave unsatisfactory results in our laboratory. It does not seem unreasonable to suggest that these discordant results with Phadebact and SeroSTAT may be simply due to the fact that such results do occur among laboratories, even when the same isolates and protocols for such evaluations are used (Guinet et al 1982).…”

Direct detection of groups A, C and G streptococci in clinical specimens by a trivalent colour test

“…Factors with properties similar to protein A are sometimes found in other organisms, notably streptococci (31), and although none of the strains used here was definitely known to carry them it is likely that some were included; no problems were observed. Streptococcus pneumoniae cultures have been shown to possess antigenic components that react with streptococcal group C antibodies, causing interference in other test systems (32,33). No cross reactions of this type were seen, another benefit of the extraction system employed (23,32).…”

“…Streptococcus pneumoniae cultures have been shown to possess antigenic components that react with streptococcal group C antibodies, causing interference in other test systems (32,33). No cross reactions of this type were seen, another benefit of the extraction system employed (23,32). The only potentially undesirable reaction obtained was too weak to cause problems in normal use of the reagent.…”